Soft tissue balancing during total knee arthroplasty (TKA) has a
direct affect on patello-femoral tracking and knee range of motion,
which are necessary for a well functioning TKA postoperatively. We
report on the use of an electronic pressure sensing instrument for soft
tissue balancing of the knee before completion of all intraoperative
bone cuts, as a way to improve patellar tracking. In a retrospective
study of 99 consecutive TKAs, with intraoperative electronic instrument
guided soft tissue balancing performed, a reduction in the incidence of
lateral patellar retinacular release was found, as compared with the 100
consecutive TKAs prior to its use (5.5% v 12%, respectively). Electronic
measurement of soft tissue balancing during TKA reduced the need for
lateral patellar retinacular release.

Total knee arthroplasty (TKA) is a highly successful procedure that
can reduce pain and improve range of motion and function by correcting
angular deformities and restoring the integrity of articulating
surfaces. (1-4) Soft tissue balance and accurate patellar tracking are
an integral part of any successful TKA. Patellofemoral maltracking
remains a common complication after TKA, particularly in valgus
deformity. Over the past 3 decades, different instrumentation systems
have been developed to make the outcome of a TKA more reproducible and
predictable. (5-9) This instrumentation focused on cutting guides and
alignment tools and, more recently, on incorporating the use of computer
navigation and robotics. (10-13) These technologies rely heavily on bony
measurements and cuts to restore alignment to the damaged articulation.
They are not designed to integrate soft-tissue balancing into
consideration. This is an important limitation, because the knee is an
inherently unstable joint that depends on soft-tissue integrity and
balance to achieve stability and optimal function. Instability results
in accelerated wear of the articular cartilage, as demonstrated in the
premature osteoarthrosis seen in anterior cruciate ligament deficient
knees. (14-17)

Precision bone cuts lead to a more accurate prosthesis fit, but
they do not guarantee optimal range of motion or joint stability. A well
aligned prosthesis must also be accompanied by good ligament balance to
produce the best functional results. Otherwise, there are potential
complications involving knee instability, which may lead to aseptic
loosening, accelerated wear, and premature mechanical failure of the
reconstructed joint.

Rotational alignment, particularly of the femoral component about
the long axis of the femur, plays a critical role in determining
soft-tissue balance of the knee, as well as patellar tracking. Until
recently, three conventional referencing methodologies have been used to
dictate rotational alignment of the femoral component. They include the
transepicondylar axis, Whiteside's line, and 3[degrees] of external
rotation off the posterior condyles. Olcott and Scott (18) compared
these three intraoperative methods to determine femoral component
rotation on 100 TKA procedures. Whiteside's line, the
transepicondylar axis, and a line placed in 3[degrees] of external
rotation off the posterior condyles were used to plan the femoral bone
cuts. The medial and lateral flexion gaps were assessed for asymmetry at
90[degrees] of flexion by laminar spreader placement. (18-19) Olcott and
Scott concluded there was variable consistency in the three conventional
methods and that any single method used to determine rotation carries at
least a 10% chance of creating a flexion space asymmetry. Another
disadvantage of conventional rotation determinants is their primary
concern with bone cuts and the neglecting of soft-tissue balancing as a
secondary concern after bone resection has been completed.

The eLibra Dynamic Knee Balancing System[TM] (Synvasive, El Dorado
Hills, California) is a pressure sensor that electronically measures the
relative pressures within the medial and lateral compartments before
final bony cuts are performed. It guides femoral bone cuts to create the
appropriate rotation of the femoral component relative to the
longitudinal axis of the femur and, consequently, may reduce the
necessity of soft-tissue releases. The eLibra[R] balancing system can be
considered as a soft-tissue management tool that is complementary to
traditional bone cutting instrumentation. Previous systems such as the
Tensor/Balancer device (Stryker Howmedica Osteonics, Allendale, New
Jersey) reported comparable but not improved outcomes to existing
techniques. (20)

Before the advent of the eLibra Dynamic Knee Balancing System[TM],
the conventional methodologies dictated the bone cuts be made before
patellofemoral tracking was assessed. In cases of lateral patellar
subluxation, most surgeons relied on surgical release of the lateral
patellar retinacular tissues in order to restore optimal patellar
tracking. Though a very simple procedure, it is not a benign one. It is
often associated with the division of the lateral geniculate vessels,
risk of hematoma, and an increase in potential for avascular necrosis of
the patella. (21) We retrospectively compared 99 consecutive cases with
the use of the eLibra[R] pressure sensing device to the 100 TKA
consecutive cases prior to its use, to test the hypothesis that it would
lead to a reduction in the incidence of lateral retinacular release to
TKA.

Methods and Materials

A retrospective chart review of all patients who underwent TKA with
intraoperative use of the eLibra[R] device, by two senior surgeons
between March 3, 2008, and August 20, 2009, was conducted to analyze the
incidence of lateral patellar retinacular release. All patients
underwent a traditional parapatellar approach. After the initial distal
femur and tibial cuts, the eLibra[R] soft-tissue force sensor (El Dorado
Hills, California) was positioned in the joint between the femur and
tibia, and the pressures of the medial and lateral compartments were
balanced. At this point, an instrument-guided accurate completion of the
remaining cuts was performed. All patients received a nonconstrained
cruciate-retaining TKA implant, manufactured by Encore Medical
Corporation (San Jose, California). After implantation of components and
reduction of the patella, the tourniquet was deflated, and the knee was
tested for full range of motion. When confronted with patellar
subluxation, a lateral retinacular release was performed to improve
patellar tracking. Data collected included gender, date of birth, date
of surgery, preoperative diagnoses, operative side, use of eLibra[R],
and surgical lateral retinacular release. A retrospective review of 100
consecutive TKAs performed before March 3, 2008, was conducted to find
the incidence of lateral retinacular release prior to the use of the
eLibra[R] system. Fisher's exact test was used to compare the rates
of lateral release between the different groups. The study was approved
by the Institutional Review Board (IRB).

[FIGURE 1 OMITTED]

Results

Between March 3, 2008, and August 20, 2009, 84 patients underwent
99 TKA (including 15 bilateral) procedures, with intraoperative use of
the eLibra[R] balancing system (Fig. 1). There were 33 males and 51
females, with an average age of 70.9 years (44.3 to 93.0) (Table 1). All
patients had a preoperative diagnosis of osteoarthritis (OA), with three
patients noted to have posttraumatic OA and two patients developing OA,
secondary to septic arthritis. There were 41 operations performed on the
left knee and 58 performed on the right. Of the 99 TKA performed with
the use of the eLibra[R], five lateral retinacular releases were done
(5.05%). On review of 100 consecutive TKAs performed by the same authors
before the use of the eLibra[R] system, the incidence of lateral
patellar retinacular release was 12% (Table 2). There was no significant
difference between the incidence of moderate and severe (angle >
15[degrees]) varus and valgus knee deformity between the two cohorts,
which were compared in the study. After analysis with Fisher's
exact test, a statistical significant difference in the rate of lateral
release was found between both groups (p < 0.05).

Discussion

Over the past 3 decades, there have been significant improvements
in the precision of bone cuts while the soft-tissue balancing aspect of
TKA surgery has been left more to that of an "art form."
Conventional methods and instrumentation have been focused on bony
alignment, with adjustments to soft tissue performed empirically when
deemed necessary. These adjustments are made based on subjective methods
of testing, and different surgeons have varying thresholds for
intervention in soft-tissue balancing. Furthermore, the surgical
approach also has been found to increase the incidence of lateral
retinacular release. (22) Bindelglass and Vince (23) reported a
decreased need for lateral release with a subvastus approach (27.5%),
compared to a parapatellar approach (51.0%). In the current
retrospective study, the rate of lateral retinacular release decreased
from 12% to 5.5% (p < 0.05), with the intraoperative use of the
eLibra[R] pressure sensor.

There is great variability within the literature as to the
incidence of lateral retinacular release during TKA. Stern and
colleagues (24) reported on 134 knees that had a preoperative alignment
of 10[degrees] or more of valgus. They found a lateral retinacular
release necessary in 76% of the arthroplasties performed secondary to
intraoperative lateral subluxation of the patella. This percentage does
not represent an average for experienced TKA surgeons but does indicate
the difficulty that valgus-deformed knees present. Benjamin and Chilvers
(25) reported on 99 patients that were not treated with lateral
retinacular release, despite medial patellar lift-off. They concluded
that patients with medial patellar lift-off at the time of arthroplasty
do not appear to require lateral release to yield acceptable
postoperative patellofemoral alignment. Fithian and coworkers (26)
conducted a scientific survey among experienced knee surgeons who had a
specific interest in the patellofemoral joint and found that they
reported a 2% rate of lateral retinacular release. However, Kusuma and
associates (27) reported a 28% lateral retinacular release rate on 1108
TKA. So, clearly, surgeons are performing these releases more often than
they report.

As there is much variability in the incidence of lateral
retinacular release, there is also confounding results reported on the
complications of the procedure. Kusuma and colleagues (27) found no
statistically significant difference in range of motion, Knee Society
score, or postoperative complications of patella fracture, subluxation,
postoperative manipulation, or wound complications. Scuderi and
coworkers (28) demonstrated, in a prospective study, the compromise of
patellar viability using technetium-99m. They reported a greater
incidence of transient patellar hypovascularity associated with lateral
release. Ritter and associates (29) reported increased patellar fracture
rates and loosening in TKAs in which a lateral release was done.

It is the authors' belief that a lateral retinacular release
is not a benign procedure and should be used only when all other options
have been exhausted. In this retrospective study, the rate of lateral
retinacular release decreased from 12% to 5.5% with the intraoperative
use of the eLibra[R] pressure sensor. Using the eLibra[R] technology as
a soft tissue management tool gives the surgeon an objective measurement
for soft tissue balancing. It bases femoral rotation on soft tissue
balance, which leads to better patellofemoral tracking and decreased
incidence of lateral retinacular releases.

Disclosure Statement

None of the authors have further financial or proprietary interest
in the subject matter or materials discussed, including, but not limited
to, employment, consultancies, stock ownership, honoraria, and paid
expert testimony.